Hitherto, as magenta color image forming couplers, there are known 5-pyrazolones (as described in, for example, U.S. Pat. Nos. 2,343,703, 2,369,489, 2,600,788, 2,908,573, 3,062,653, 3,519,429, 4,080,211, etc.), pyrazolobenzimidazoles (as described in, for example, British Patent No. 1,047,612, etc.), indazolones (as described in, for example, U.S. Pat. No. 3,770,447, etc ), and pyrazolo [5,1-C][1,2,4]-triazoles (as described in, for example, U.S. Pat. No. 3,725,067, etc.).
Also, various kinds of so-called 2-equivalent couplers that a so-called coupling off group, i.e., a group capable of being released by causing a reaction with the oxidation product of an aromatic primary amino color developing agent is bonded to the coupling active position of the skeleton of each of the foregoing couplers for reducing the amount of silver used and controlling the coupling rate have been proposed (as described in, for example, U.S. Pat. Nos. 3,227,554, 3,311,476, 3,419,391, 3,926,631, 4,241,168, 4,076,533, 4,146,396, 4,237,217 and 4,351,897, Japanese Patent Publication No. 34044/78, etc.).
Also, recently, magenta color image forming couplers having a blocking group bonded to the oxygen atom of an enol in the state that the 5-position of 5-pyrazolone is enolated at the position capable of reacting with the oxidation product of an aromatic primary amino color developing agent (as described in, for example, Japanese Patent Application (OPI) No. 135841/81 (the term "OPI" indicates an unexamined published patent application open to public inspection)) and magenta color image forming couplers having a blocking group bonded to the cyclic nitrogen atom of the above-described pyrazolobenzimidazole or imidazolone 1H-pyrazolo [5,1-C][1,2,4]-triazole at a position capable of reacting with the oxidation product of an aromatic primary amino color developing agent (as described in, for example, Japanese Patent Application (OPI) No. 133734/81) have been proposed.
For improving the properties of the latter couplers, various compounds having the same skeletons as the foregoing magenta color image forming couplers and improved blocking groups have been proposed (as described in, for example, Japanese Patent Application (OPI) Nos. 107537/83, 107538/83, 111034/83, 111035/83, 111036/83, 111943/83, 111944/83, 113937/83, 113939/83, 113936/83, 113938/83, 113940/83, 115437/83, etc.). The feasutes of the couplers having these blocking groups are that since one of the dissociative hydrogen atoms of the above-described 4-equivalent magenta couplers or 2-equivalent magenta couplers is blocked by the block group, the magenta color image forming coupler is stabilized to heat, light and oxidation and the coupling rate can be controlled in a manner different from the 2-equivalent couplers. Now, since the above-described couplers have a blocking coupler which can be released by causing a reaction with the oxidation product of an aromatic primary amino color developing agent, silver halide is excessively consumed by 2-equivalent couplers in other stages than the color image forming stage and hence attempts to use such a coupler are not a desirable direction from the viewpoint of saving resources. However, in the case of applying these couplers to everprogressing silver halide color photographic materials for photographing, it becomes an advantage for improving the graininess of the color photographic materials for photographing that silver halide is excessively consumed by 2-equivalent couplers for other purposes than the formation of color images. That is, the foregoing coupler has the advantage that the excessive oxidation product of a developing agent formed at developing exposed photographic materials for photographing usually forms a large amount of dyes to reduce the graininess of images formed but in the case of using the couplers, the silver halide captures the excessive oxidation product of the developing agent, whereby the graininess is improved.
In spite of these excellent principles, the conventional magenta color image forming couplers having a blocking group still have deficiencies in that they are unstable for practical use, they show low colored dye images, and the colored dye images formed by using these couplers are poor in fastness.